The invention is in the field of electronic reproduction technology and is directed to a method and to a circuit arrangement for signal processing in an electronic engraving machine for engraving printing cylinders for rotogravure.
In an electronic engraving machine, an engraving element having an engraving stylus as a cutting tool moves along a rotating printing cylinder an in axial direction. The engraving stylus controlled by an engraving control signal cuts a sequence of depressions, called cups, arranged in a rotogravure raster into the generated surface of the printing cylinder. The engraving control signal is formed in a signal editing unit by superimposition of an engraving signal representing the gradations between xe2x80x9cblackxe2x80x9d and xe2x80x9cwhitexe2x80x9d with a periodic raster signal (vibration). Whereas the raster signal effects a vibrating lifting motion of the engraving stylus for generating the raster, the engraving signalxe2x80x94in conformity with the gradations to be reproducedxe2x80x94controls the cut depths of the cups engraved into the generated surface of the printing cylinder.
Among the things occurring in the signal processing unit are a calibration of the engraving signal to the cut depths of the engraving stylus for xe2x80x9clightxe2x80x9d (white) and xe2x80x9cdarkxe2x80x9d (black) and the superimposition of the corrected engraving signal with the raster signal for generating the engraving control signal.
In a traditional signal processing unit, the signals are processed in analog fashion in that the input signals are supplied in digital form, are digital-to-analog converted and operated with one another in analog networks, whereby the resulting signal is then amplified in an analog amplifier and is output as an engraving control signal for the engraving element.
Signal processing with analog networks has the disadvantage that the transfer behavior of the networks cannot be optimized without further ado and, due to tolerances and temperature dependencies of the components, is not stable enough in order to generate a good engraving quality.
WO 96/34746 already discloses a method for digital signal processing in an electronic engraving machine, whereby engraving data that represent the gradations to be engraved and function value data that define the periodic raster signal are converted into engraving control data according to a transfer function.
An object of the present is invention to improve a method and a circuit arrangement for signal processing in an electronic engraving machine for engraving printing cylinders for rotogravure such that the signal processing can be optimized in a simple way in order to achieve a good engraving quality.
According to the method and apparatus of the present invention, for a signal processing in an electronic engraving machine for engraving a printing cylinder for rotogravure with an engraving element controlled by an engraving control signal, a digital transfer function is formed whereby at least one of the transfer function and transfer coefficients of the transfer function are modified by control data. The transfer function is modified by setting parameters for calibrating gradations xe2x80x9cblackxe2x80x9d and xe2x80x9cwhitexe2x80x9d to be engraved. Correction data for cut depth correction of the engraving element are provided dependent on at least one of engraving data and control data. The transfer function is additionally corrected by the correction data for compensating a mechanical wear of the engraving stylus. Engraving control data are generated according to the transfer function from engraving data that represent gradations between xe2x80x9cblackxe2x80x9d and xe2x80x9cwhitexe2x80x9d to be engraved and from function value data that represent a periodic raster signal for generating a raster. The engraving control data are converted into said amplified analog engraving control signal. An engraving stylus of the engraving element controlled by the engraving control signal engraves a sequence of cups arranged in the raster into the printing cylinder, and the engraving element executes a feed motion along the printing cylinder directed in an axial direction of the printing cylinder for engraving of the cups.